Refactored to allow ConceptEvaluator

docs/syntax_v3.md

@@ -1,6 +1,10 @@
+In this example, I try to think of how I can deal with errors
 ```
 > "hello
 -> unfinished quote "
+
+create a concept to recognize the error
+
 > def concept unfinished quote q
 ... where:
 ...... q in ('"', '"')
@@ -9,9 +13,16 @@
 ... input = sheerka.last_input
 
 
+Create the rule to manage the error
+
 > when unfinished quote q as c:
-... add rule as:
-...... if q in sheerka.input:
+... add rule r as:
+...... if q is last of sheerka.input:
 ......... sheerka.resume(c, c.input + input)
-......... remove rule 
-```
+......... remove r 
+
+def concept a is last of b as:
+    where b is list
+    as b[-1] == a
+```
+